For example, Japanese Patent Application Publication No. 2009-230921 (hereafter called “Document 1”) discloses an electromagnetic opening/closing device as a prior art. In the device described in Document 1, a relay unit (an electromagnetic relay) is put in a case made from synthetic resin, and a pair of main terminals and a pair of coil terminals are protruded from the case. The pair of main terminals is connected to contacts of the relay unit, and the pair of coil terminals is connected to a coil for an electromagnet of the relay unit. In addition, the pair of main terminals is connected to a power supply line from a power supply to a load(s). The relay unit (the electromagnetic opening/closing device) is turned on when an excitation current flows between the pair of coil terminals, while the relay unit (the device) is turned off when no excitation current flows between the pair of coil terminals. That is, the electromagnetic opening/closing device is turned on, thereby closing the power supply line from the power supply to the load, while the device is turned off, thereby opening the power supply line.
In such electromagnetic opening/closing devices, the conduction between contacts (a stationary contact and a moving contact) may be impaired due to surface oxidation thereof, or the stationary contact and the moving contact may be welded to each other due to arc. Conventionally, apparatuses equipped with such an electromagnetic opening/closing device require to detect various malfunction generated in the device.